Metallization by cathode disintegration



June 2 1939- w. BURKHARDT El" AL 2,163,430

METALIZATION BY CATHODE DISINTEGRATION Filed Feb. 18, 1937 d v 5 1W fk h /Ja) Um m l Y w w w Patented June'Zll, 1939 PATENT OFFICE METALLIZATION BY CATHODE DISINTE GRATION Wilhelm Burkhardt, Berlin-Grunewald, and R11- doll Iteinecke, Berlin-Lankwitz, Germany, assignors to Bernhard Berghaus, Berlin-Lani:-

witz, Germany Application February 18, 1937, Serial No. 126,504

In Germany February 21, 1986 7 Claims.

The metalization by cathode disintegration has the disadvantage that a portion of the particles leaving the cathode returns thereto, whereby the efllciency is reduced. The cathodes have hitherto been. used in the form of .a band, metal sheet, plates, tubes or wires. When the cathode is in the form of a wire, the diameter of which is comparable with the length of the free path of the gas molecules, a much smaller number of vaporised. metal atoms find their way back to the cathode as compared with a large flat cathode, the' number thereof being the smaller the smaller the diameter of the wire, (see'A. Giintherschulze in the Zeitschrift fiir "Technische Physik 1927, pages 169 to 178, and more particularly righthand column on page 174). Thus, according to -Giintherschulze, the partial pressure of the gas in front of the cathode, and therewith, also, the amount reaching the anode, must increase with the decrease of the diameter of the wire. In this known method heated cathodes are also known, since in the cathode distintegration the wires are heated by themselves and reach incandescent temperatures.

According to page 171, left column, chapter 3, paragraph 1, it is known that the cathodes become hot, by the heating of the electric current. This arrangement of thin cathode wires of the order of the length of the free path, which according to Giintherschulze is known, forms the basis of a subsequent Austrian patent specification No. 136,250 of 1932, which relates to a method of metalizing by cathode disintegration, the essential feature of which is, that use is made of heated electrodes, the thickness of which is of the order of the length of the free path of the metalatoms. In this known method use may be made of a large number of thin wire or hand-like electrodes. On the other hand, more recent experiments have shown that the most favourable wire thickness is not dependent upon the length of the free path, as it is assumed in the Austrian patent specification. Further, according to the latter, it should be possible, in the metalization by cathode disintegration, to accelerate the disintegration when the cathodes are heated.

However, the disintegration experimentsmade in this direction with resistance-heated cathode wires, more particularly of metals which disin-' tegrate with difliculty, revealed an important disadvantage in connection with the usual meth- 0d: the temperature of. the cathode wires, in order integration, more particularly in .the case of materials which are disintegrated with difiiculty,

such as tantalum, chromium, tungsten and their compounds and carbides, for metallurgical purposes, must reach a very high degree, which requires large heating currents, which, in their turn, produce very disturbing magnetic fields around the wires. Owing to these magnetic fields, which increase in a hyperbola-like manner with respect to the cathode surface, the paths of the electrons and ions (the latter disintegratethe cathode when they impinge upon it) are also increasingly deflected in the longitudinal direction of the oathode wires. These movement components of the charge carriers, which run in a direction at rightangles to the direction of distintegration, prevent an increase in the intensity of disintegration taking place.

The above mentioned disadvantages are re moved almost completely by the present invention, which relates to a method of metalization by cathode disintegration, by means of heated cathodes, and which consists in that, for the heating of the cathode, in order to reduce the deflection of the charge carriers produced by the magnetic fields of the cathode heating currents, use is made of an alternating current. For the disintegration of the cathode use ispreferably made of a pulsating direct current voltage. Pref- I erably, the heating of the cathode is effected by means of an alternating current voltage, and the disintegration of the cathodes by means of a pulsating direct current voltage, the maximum. values of which occur when the heating voltage reaches its minimum values. The cathodes to be disintegrated may, preferably, consist of metals fusing at a high temperature, such as,. for instance, tantalum, chromium, tungsten' and the like and their compounds. The wave of the pulsating direct current voltage may preferably be so chosen that its minimum values do not fall belowthe extinguishing voltage, which corresponds each time to the path of the discharge.

Further, the deflection of the discharge carriers is reduced by using wires for the cathodes, the current in the successive wires being each time reversed with respect to one another. The cathode wires may be provided with a core of a metal fusing at a higher temperature as compared with'the metal to be disintegrated. This has the advantage that the fusing point of the metal to be disintegrated can be approached to a greater extent, without being afraid that the wire will break. The cathode wires may be connected in series or in two parallel rows, which are displaced relatively to one another and connected in parallel'in oppositefdirections. Further, the

may be supported by insulating bars.

Further, according to the invention, instead of the uninterrupted heating of the cathode for the purpose of reducing the deflection of the charge carriers produced by the magnetic fields of the cathode heating currents, by means of an alternating current, use may preferably be made of a periodic heating. Thus, use is made, not only of an alternating current but of a periodic heating. For the periodic heating use may advantageously be made of a pulsating direct current. The individual impulses or maximum values of the heating current -lie preferably between those of the disintegration voltage with respect to time. The pulsating direct current for the heating may, with advantage, consist of an intermittent direct current. The intermittent direct current represents a limit case of the pulsating direct current, in so far as the voltage drops down to nil, so that a current interrup tion takes place between the individual impulses. The duration of the interruption in which the disintegration takes place, without being hindered by detrimental magnetic fields, depends upon the nature of the cathode material and its heat capacity. The heating impulses and the intervals of rest may be different with respect to time. Preferably, the duration of the heating is chosen small with respect to that of the disintegration. For the disintegration voltage use may preferably be made of an intermittent direct current voltage. The heating and the disintegration of the cathode may advantageously take place alternately.

For the heating of the cathode wires use may thus be made of pulsating or intermittent direct current, for instance, in the form of a half-wave of an alternating current voltage, in such manner that these half-waves lie between the maximum values of the disintegration voltage as regards time. If the same is, for instance, a direct current voltage obtained by a double rectification of an alternating current voltage'of 50 periods and pulsating with 100 periods, the cathode heating is preferably effected only by one half-wave of an alternating current voltage of 100 periods obtained by half rectification, or also by a pulsating direct current voltage, the superposed alternating current voltage of 100 periods of which is displaced in phase through 90 with respect to the disintegration voltage.

The disintegration voltage may also consist of a half-wave of an alternating current voltage of, for instance, 50 periods, which is preferably superposed on a direct current voltage, the value of which is not below the extinguishing voltage. The heating of the cathodes then takes place only by means of a half-wave of an alternating current voltage, also of 50 periods. In both examples the alternating current voltage halfwaves, serving for the heating of the cathodes, lie between the half-waves or maxima of the intermittent or pulsating disintegration voltage.

If it is desired to obtain a still sharper time separation between the heating and the disintegration voltage, than it is possible to obtain by sinusoidal intermittent or pulsating voltages, use may be made of intermittent voltages of rectangular or trapezoidal form as can be obtained, for instance, by means of valve tubes with a saturation characteristic. By using pulsating, preferably intermittent heating currents, and disintegration voltages of the cathodes, the advantage is attained that, owing to the unin- .cathode wires, which are placed horizontally,

terrupted heating currents, no deflection of the charge carriersoccur during the disintegration. One arrangement for carrying themethod into effect comprises a source of alternating current required for the maximum disintegration by the glow current only.

The accompanying drawing illustrates, by way of example, various modes of carrying the invention into effect.

Figure 1 is a section through a cathode wire provided with a core;

Figure 2 is a vertical section through the support of horizontally-suspended cathode wires;

Figure 3 is a horizontal section through four cathode wires which are traversed by a current in the same direction;

Figure 4 shows a horizontal section through four other cathode wires, in which the current flows in opposite directions in alternate wires;

Figure 5 is a diagrammatic illustration of the cathode wires connected in series;

Figure 6 shows the parallel connection of the cathode wires;

Figure 7 is a diagram showing the course of the pulsating direct current voltage for the cathode disintegration, and of.the alternating current voltage for the heating of the cathodes;

Figure 8 is a diagram of connections of an arrangement for the heating of the cathodes by means of an alternating current voltage, and for the disintegration of the cathodes by means of pulsating direct current voltage.

Referring to Figure 1, which is a section through a cathode wire provided with a core, K is the cathode material to be disintegrated and d is the core. Since the wires may reach the flow limit, owing to the use of the high temperatures, they are preferably provided with a thin core of a metal fusing at a higher temperature than the metal to be disintegrated. The metal core of higher fusing point may, according to the nature of the metal to be disintegrated, consist, for instance of tantalum, chromium, tungsten or the like.

Referring to Figure 2, which illustrates the support of the horizontally suspended cathode wires, s are the bus bars, between which the cathode wires K are suspended, preferably horizontally. The cathode wires are supported by a number of insulating bars, for instance of porcelain, which may form a rigid frame b. With such a suspension arrangement use may be made of wires without a wire core having a higher fusing point.

Figure 3 shows a cross-section through four cathode wires which are traversed by a current in the same direction, the fields H1 of which are combined to a total field Hz, which, according to the direction of the charges, imparts a greater deflection to their paths as compared with the arrangement shown in Figure 4, which illustrates a cross-section through four cathode wires, in which the current flows in opposite directions area-rec in alternate wires. Inview oi the fact that the direction of the heating-current in' successive cathode wires is alternately reversed, the total magnetic field Hz around the cathode wires, considered as a whole, disappears, so that the fields Hi can be formed.

Figure 5 shows an arrangement of cathode wires K connected to the voltage Us arranged opposite the anode a. In this arrangement the heating current flows in the opposite direction through adjacent wires.

Referring to Figure 6, K are the cathode wires connected in parallel and arranged opposite the anode a, the said cathode wires being connected to the heating voltage Us. two rows of cathode wires connected in parallel are formed, which lie in the same plane, and each of which is connected to two bus bars. The two rows are connected in parallel in opposite directions, so that the current is reversed in adjacent wires. In the arrangement according to Figures 5 and 6, a magneticfleld according to Figure 4 is produced. The arrangements of the cathode wires according to Figures 5 and 6 may also be used in conjunction with the horizontal arrangement according to Figure 2.

Figure '7 is a diagram showing the course of the pulsating direct current voltage Uefor the In this arrangement a cathode disintegration and of the alternating current voltage Uh for theheating of the oathodes. It will be seen from this diagram that, when the heating voltage Uh reaches its maximum, the disintegration voltage U. reaches its minimum and vice versa, when the heating voltage Uh passes through the zero point the disintegration voltage Ua reaches its maximum.

The disturbing-efifect of the magnetic fields produced by the heating current of the cathode wires is reduced to a minimum by that a'pulsating direct current is used for the anode current effective in the path of discharge and an alternating current for the cathode heating, in such a manner that the maxima of the heatlngcurrent In occurs when the discharge current Ia reaches its minima, whilst at the time of the maximum of the discharge current the heating current passes through zero.

Figure 8 shows a diagram of connections of an arrangement for the disintegration of the cathodes by means of a pulsating'direct current voltage, and for the heating of the cathodes by means of an alternating current voltage. The

' arrangement consists of a source for the pulsating direct current voltage Up. and of a source of alternating current voltageUa-ior the heating. The disintegration current is obtained ina known manner, for instance, by a double rectification of a single phase alternating current, as is indicated diagrammatically by the rectifying device 9. The natural wave of the first harmonic of the alternating current voltage of 67% superposed on the direct current component may be reduced, as desired, by a filter, consisting of achoke L and a condenser C. The minimum of the disintegration voltage Us may advantageously be so chosen, that it does not lie below the extinguishing voltage which prevails at the time in the discharge path.

The heating alternating current voltage Us which is displaced in phase through 90 with respect to the alternating current voltage supplying the pulsating anode direct current voltage Us, may, for instance, be derived 'over a transformer it, from a phase of a three-phase transformer j, which is star connected, whilst the other two phase voltages supply the anode disintegration voltage Us over a transformer by geometric subtraction.

Since the two consuming parts, viz., the disintegration and the heating, constitute almost pure ohmic loads, the phase displacement of 90 between the disintegration current Ia and the heating current In is attained with sufficient accuracy.

The arrangement illustrated in Figure 8 is,

given only by way of example. It is to be understood that the pulsating direct current for the disintegration, and the alternating current for the heating, may be obtained in any other known manner, and be relatively adjusted as desired.

What we claim is: l. A method of metalizlng by the disintegration of heated cathodes, consisting in effecting the heating and the disintegration of the cathode alternately by two separate currents alternately and repeatedly applied thereto, whereby the deflection of the chargvcarriers produced by the magnetic fields of the current heating the cathode is reduced.

2. A method as claimed in claim 1, consisting in effecting the heating of the cathodes by means of analternatlng current.

3. A method as claimed in claim 1, consisting in effecting the heating periodically by means of a pulsating direct current.

4. A'method as claimed in claim 1, consisting in effecting the heating periodically by means of an intermittent direct current. Y

5. A method as claimed-in'claim 1, consisting in effecting the disintegration of the cathodes by means of a pulsating direct current voltage.

6. A method as claimed in claim 1, consisting in effecting the heating of the cathodes by means of an alternating current, and the disintegration of the cathodes by means of a pulsating direct current voltage, the maxima of which occur at the points where the alternating current used for the heating of the cathodes changes its direction.

7. A method of metalizlng by the disintegration of heated cathodes as claimed in claim 1 consisting in effecting the disintegration of the cathodes by means of a pulsating direct current voltage.

WILHELM BURKHARDT. RUDOLF REINECKE. 

